Cryogenic Valve design Tips(Extended Bonnet)
C Tech Science and Technology Co., Ltd has accumulated rich design and production experience in the past few years. On the basis of MESC SPE 77/200, We also did some more improvements during the real design and production.
Cryogenic Valves shall be supplied with extended bonnets, meeting the minimum vapour space requirements as per MESC SPE 77/200. The length of the extension bonnet shall be sufficient to maintain the stem packing at a temperature high enough to permit operation within the normal temperature range of the packing material. This used to prevent the up stem packing from icing during the application.
For rising stem valves, the vapour space is defined as the distance between the bottom of the packing box and the top of the lower bon net bush. For quarter turn valves, the vapour space is defined as the distance between the bottom of the packing box and the top of the lower stem bearing.
Each extended bonnet shall be provided with an insulation drip plate. The drip plate shall be clamped-on the extended bonnet with the bolting on the upper side to enable easy adjustment. C Tech Company has improved the original drip plate with flow groove which was already successfully used for the cryogenic application. The gap between the bonnet and the collar plate shall be sealed to avoid condensation entering into the insulated area. The diametrical clearance between the stem and the extended bonnet housing shall be minimised to reduce convective heat losses.